In this thesis, a new synthetic methodology for the high yield synthesis of spineltype
transition metal ferrite nanoparticles has been developed. This approach is based on
the complexation of the first-row transition metal cations with diethylene glycol (DEG)
followed by the hydrolysis of the resulting chelate iron alkoxide complexes in the
presence of an alkaline hydroxide. Due to the passivation of their surfaces with DEG
molecules, the as-prepared nanoparticles are stable against agglomeration and can be
easily dispersed in polar protic solvents (water, alcohols, etc.). Alternatively, a postsynthesis
passivation with carboxylate ions can render the iron oxide nanocrystals highly
dispersible in non-polar solvents. Optimization of the reaction conditions suggested that
the size of the nanocrystals could be controlled by changing the complexing strength of
the reaction medium. This hypothesis was verified in the case of the Fe3O4 nanoparticles:
their sizes vary from 5.7 nm when the reaction is performed in neat diethylene glycol to
16.8 nm in N-methyl diethanolamine (NMDEA), whereas a 1:1 (%wt) mixture of these
solvents yields nanocrystals with an average size of and 12.7 nm. A detailed
characterization by using a wide variety of techniques, including powder X-Ray
diffraction, IR spectroscopy, thermogravimetric analysis (TGA), transmission electron
microscopy (TEM) and 1H-NMR spectrometry was performed in order to elucidate the
composition and the morphology of the variable-sized iron oxide nanoparticles. Both
finite size and interparticle interaction effects were identified to influence the magnetic
behavior of the oleate-capped nanosized particles. At low temperatures the Fe3O4
nanocrystals exhibit a ferromagnetic behavior with blocking temperatures which increase
with the average particle size, whereas at room temperature, except for the largest
nanoparticles, they undergo a superparamagnetic relaxation. We exploited the high
surface reactivity of the 10 nm Fe3O4 nanoparticles to attach 2-3 nm gold grains to their
surfaces through a simple, two-step chemically controlled procedure. By chemically
bonding bioactive molecules to the attached Au nanoparticles these novel nanoarchitectures
open up new opportunities for the implementation of the magnetic
nanoparticles as a platform for various applications in the biomedical field.

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